1. Technical Field
The present invention relates to a mobile communication system and a link establishment method, more specifically to the mobile communication system and the link establishment method for establishing a link of an X2 interface based on a 3GPP specification between a plurality of base stations connected to an IP network.
2. Description of the Related Art
LTE (Long Term Evolution), discussed in 3GPP (3rd Generation Partnership Project), is a next step developed from an HSDPA (High Speed Downlink Packet Access) which is currently in service, or of an HSUPA (High Speed Uplink Packet Access) which is discussed to be in service in a later stage, and is also referred to as S3G (Super 3G) or EUTRA(N) (Evolved UMTS Terrestrial Radio Access (Network)). The characteristic is to reduce packet transmission delay and to provide a high speed data system in which the packet is optimized.
In a wireless communication system based on 3GPP-LTE, instead of a combination of a wireless control device (RNC: Radio Network Controller) of an existing 3G system and a basestation device (Node B), an enhanced Node B (hereinafter referred to as eNB) is added. In addition, a new communication interface (hereinafter referred to as X2 interface) is added for providing a connection between the eNBs. The reason for the addition is that a user (U-Plane) signal and a control (C-Plane) signal are directly transferred via the X2 interface during a handover between adjacent eNBs.
FIG. 8 is a diagram showing a configuration example of the mobile communication system based on the 3GPP specification. In FIG. 8, “S1IF” indicates an S1 interface, and “X2IF” indicates an X2 interface. This system includes a mobile stations (MS), a base stations (eNB), a router, not shown in the figure, which configures an IP network 100, an access gateway (aGW) and the like. Each node (eNB, router, aGW and the like) is connected to each other with, for example, a wired IP line in order to transmit the U-Plane signal and the inter-station control (C-Plane) signal with call processing.
In the system based on 3GPP-LTE, the interface between the IP network (core network) and the eNB is defined as an S1 interface, and the interface between the eNBs is defined as an X2 interface. The existing system did not have the X2 interface. The X2 interface is newly added in the 3GPP-LTE in order to transfer the U-Plane signal and the C-Plane signal during handover. Another difference from the existing system is that a GPS (Global Positioning System) receiving unit 11 is implemented on each eNB. According to such configuration, the IP network 100 is connected to each eNB via the S1 interface. In addition, a link of the X2 interface has to be established between all the adjacent eNBs performing the handover.
The mobile communication system is known, in which a plurality of base stations each inform their own system information to each other by a multicast packet. In addition, the mobile communication system is capable of broadcasting broadcast information to a mobile station without a wireless control device (RNC) by forming the broadcast information autonomously and distributively in each base station, for example see Japanese Laid-Open Patent Publication No. 2002-209275.